Saturday, September 29, 2007

We've had a pretty good run of nice weekends here in Southern MB in September, with some of the warmest days this month falling on the weekends. And it looks like we'll have another nice day today with gusty southerly winds sending temperatures into the mid twenties.. some 10 degrees above normal for the end of September. Those southerly winds will increase by early afternoon with gusts to 60 km/h likely especially through the Red River valley which tends to funnel southerly winds. That should strip off a few more leaves today! A cold front will move through tonight bringing possible showers with clearing and cooler, but still pleasant conditions for Sunday. Nice weather should continue into the first few days of October. Get out and enjoy these last nice days of autumn! (hopefully we get a few more in October.. and even November!)

Monday, September 24, 2007

A band of showers and thunderstorms brought locally heavy rain to the Winnipeg area last night, resulting in the most significant rainfall in many areas since July 25th. Much of the city picked up at least 20 mm of rain, most of it falling around 1 am with thunderstorms. At my station, I picked up 22 mm of rain with a peak rainfall intensity of 80 mm/hr at 1 am. Here is a roundup of Winnipeg and area rainfall amounts since midnight. (All but the Forks are unofficial amounts from local private weather stations.)

Sunday, September 23, 2007

For the second Sunday in a row, summerlike temperatures spread into Southern MB, with 30 degree heat along the US border. Emerson was the national hot spot with a sizzling 32.4C temperature as of 5 pm, with Sprague and Gretna registering 31C temperatures. Winnipeg was also on its way to possibly hitting 30C today, but a cold front came through around 3 pm, with winds shifting into the northeast bringing cooler air from the interlake, knocking temperatures down from 27C to 22c between 3 and 4 pm.

For tonight a band of showers and possible thunderstorms is expected to move across southern MB from the southwest. Models are suggesting between 10 and 20 mm of rain over much of the Red River valley by morning including Winnipeg with some locally heavy rain at times thanks to embedded shower or thunderstorm activity moving up from North Dakota. Hopefully, this rain materializes and doesn't miss us, as has been the case the past couple of months. Look for a blustery and much cooler day Monday with cloudy skies, occasional light rain or drizzle, and temperatures only around 10C. Welcome to the roller coaster weather of fall!

Wednesday, September 19, 2007

A weather system tracking across the northern US plains will spread an area of showers across southern MB on Thursday hopefully bringing some much needed rainfall to the south Winnipeg area. Current indications are that between 5 to 10 mm of rain is expected across Winnipeg, although some model solutions indicate as much as 20 mm of rain is possible (more likely with embedded thunderstorms) . This would be most welcome across southern Winnipeg which has been very dry since late July. Lawns here are brown and cracked with a severe lack of subsoil moisture. Here in Charleswood, I've only recorded 26 mm of rain since August 1, with no single rainfall over 5 mm over that time. The last time we had more than 5 mm of rain at one time was way back on July 25th during a heavy thunderstorm when 18 mm fell. So a little rain Thursday wouldn't be such a bad thing..we could sure use it.

Tuesday, September 18, 2007

The Elie, MB tornado of June 22, 2007 (image left) has been re-classified as an F5 tornado, upgraded from its original F4 rating. This makes the Elie tornado Canada's first officially documented F5 tornado. The re-classification was based on re-analysis of the video data, including video of a home being completely swept off its foundation and obliterated in mid air as well as a heavily loaded van being thrown a considerable distance. (see video here) According to the Fujita tornado rating scale, this type of damage is consistent with an F5 tornado with wind speeds of 400-500 km/h. For further details on the Elie, MB tornado.. see my earlier June blog entries.

Note that tornado ratings are based on the most intense damage found within the track of that tornado. It doesn't mean the tornado was always at F5 strength, but that it reached F5 at its maximum intensity. Note also that tornado strength is based on physical damage caused by the tornado. If a powerful tornado doesn't hit or damage anything, than it can only be classified as an F0 tornado.. no matter how strong it really may have been. As a result, there may have been other tornadoes in Canada that were F5 strength at some point, but they didn't hit any structures during that time to warrant an F5 rating. The Pipestone tornado that hit a day after Elie is a good example of this. This monster tornado is officially rated as an F3, however it didn't hit anything structural at its maximum intensity, staying mostly over open fields and forests at its height (good thing too!)

Just a note to advise you that I'm currently experiencing problems with my humidity and dew point readings from my weather station. They are registering way too low compared to actual conditions. For example, today we are seeing humidity values around 95-100% around Winnipeg but my station is showing only 50%. Also, since dew points are calculated from the humidity reading, they are also too low. I've ordered a new temperature/humidity sensor that should fix the problem, but that will take a couple of weeks or so before I get it. Until then, ignore my humidity readings, and check on nearby Pacific Junction school for more accurate Charleswood humidity values.

Monday, September 17, 2007

It was another balmy summer-like day over southern MB with sunshine and temperatures in the mid 20s along with dewpoints in the upper teens. The warm weather however will come to end Tuesday as northerly winds develop bringing considerably cooler air southward. That cool air was evident over central MB and the northern Interlake today with temperatures only around 10C this afternoon in Swan River under overcast skies. That cool air should be moving into Winnipeg Tuesday morning with afternoon temperatures likely only in the mid teens - some 10 degrees cooler than today's mid twenty values. Currently, the forecast high for Winnipeg on Tuesday is 22c which looks a little optimistic from what I'm seeing. Don't be surprised to see that forecast high revised downward by tomorrow.

Sunday, September 16, 2007

Wow.. what a turnaround from the cold just a couple days ago. Temperatures soared to a surprisingly warm 30 degrees in Winnipeg this afternoon, with a gusty southwest wind aiding in the warmup. At 3 pm the temperature at Winnipeg airport shot up to 30 degrees (29.9C officially) while the humidity dropped to 17% as the dewpoint went from 10 to 2c. Almost desert-like air! What a nice surprise as I thought we were done with 30C temperatures for the year. For the record, last year we had our last 30C temperature on Sept 15th, so we went one day better this year!

Interesting article in today's paper about how ice cover over the Arctic is at its lowest level on record this year. Ice cover has shrunk to about 3 million square km, a million square kilometres less than the previous record lowest year in 2005. Data from the US's National Snow and Ice data Center give slightly different numbers.. showing ice coverage at 4.2 million sq km as of Sept 10th, still the lowest on record (previous record low was 5.3 million sq km in Sept 2005) Whatever the case, it's an amazing stat.. and certainly lends strong support to the global warming theory that has always warned of this consequence. Note however that these reliable ice cover records only go back to 1978 which is not a very long record to make any definite conclusions. One has to wonder what Arctic ice cover levels were like in the years before 1978, especially in the 1930s and 40s when we had some very extreme weather, and some very mild winters.

Nonetheless, you have to figure something is definitely changing up in the Arctic, and a continual reduction of the Arctic ice cover will have major impacts on our climate, sea levels, and economy (with the possible annual use of the Northwest passage) One of the impacts of a reduced Arctic ice cap is that winters would generally be starting later, and we have certainly seen this in southern MB with 8 of our past 10 Decembers warmer than average. So it does appear that we're already seeing some impacts of this exceptional loss of Arctic ice with delayed, shorter, and less severe winters.

It's interesting to note that Winnipeg had its warmest January on record in 2006, following the last record low Arctic ice cover in the fall of 2005. Will this mean we will have another record mild winter this year? Well, it's tough to say since there are other factors which can influence our winters such as a developing La Nina, and other global climatic oscillations. However, one has to certainly consider that there is a good possibility of another warm winter coming up for Southern MB given this year's amazing loss of Arctic sea ice.

Thursday, September 13, 2007

A band of lake effect rain has developed off Lake Manitoba this morning and is currently affecting parts of west Winnipeg. Cool air (0c at 850 mb) flowing over the warm open waters of the MB lakes (16-18c) has created these bands of lake effect precipitation which should persist this afternoon into tonight. Currently low level winds are from a 300 degree orientation which is advecting the band into west Winnipeg and areas northwest. Rosser has picked up 4 mm of rain this morning underneath the band. Outside the band, the sun is shining in parts of Winnipeg!

For this afternoon and evening, models indicate low level steering winds should become more northerly, with a 330-350 orientation which should push the Lake Manitoba bands westward through Elie and Sanford and areas west. A 330-340 band off Lake Winnipeg would affect the Patricia Beach and Beausejour areas. (see example of 330 degree squalls from last October) I expect the bands to intensify this evening and tonight off both Lake Manitoba and Lake Winnipeg as a cold pool of -5C air at 850 mb moves over southern MB. This will give a 20C temperature differential between the lake water and 850 mb temperatures, which is getting extreme for lake effect precipitation (you need a minimum differential of 13c for lake effect initiation). There's even a chance that the precipitation could mix with or change to wet snow tonight into Friday morning, although I suspect the warm lake waters should maintain the precipitation mainly as rain.

The good news is that we should see a moderating trend this weekend with dry conditions and warmer temperatures as this cold pocket of air moves east.

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Lake effect update.. Interesting to see squalls starting to re-orient themsleves this afternoon as low level winds become more northerly. The 300 degree rainbands off Lake Manitoba which had been affecting Winnipeg are now weakening, while a new 330-340 band sets up further west between Elie and Portage. See attached Doppler radar image from 12:20 pm showing this lake effect transition in progress. Note also lake effect bands starting to develop off Lake Winnipeg.

Wednesday, September 12, 2007

After a brief reprieve today with temperatures close to or over the 20 degree mark over Southern MB, a cold front will push through this evening bringing in much cooler air for Thursday. Brisk northwest winds on Thursday along with cloudy skies will keep temperatures only in the single digits most of the day, with afternoon highs struggling to hit the 10c mark. There will be occasional showers as well, although amounts should be on the light side here with the bulk of the rain falling through the interlake.

Thursday night will be downright cold as 850 mb temperatures plunge to -5C. This will be cold enough to possibly generate.. wait for it.. SNOW, especially over higher elevations of Southern MB! In addition, the cold air moving over the warm lake waters (currently running around 16 to 18C over the south basins) will generate bands of lake effect precipitation to the south and southeast of Lakes Manitoba and Winnipeg Thursday night into Friday morning. The warm lake waters should keep the lake effect precipitation as rain, however there is a chance that if the instability is deep enough and the bands are intense, the lake effect precipitation could change to wet snow.

Tuesday, September 11, 2007

Brisk northwest winds have ushered in an unseasonably cool airmass over Southern MB today with temperatures only in the single digits early this afternoon. Normal highs for this time of year are around 18-19C, so we're a good 10 degrees below "normal". With an expected high of only 11c this afternoon, this will be only a couple degrees above the coldest high ever for Sept 11th which was 8.9C back in 1890. (NOTE: this is corrected from an earlier post, which incorrectly stated the coldest Sept 11 was 15.6C back in 1949.. I was looking at the wrong column!) The cool northerly winds have even produced some bands of lake effect rainshowers off Lakes Manitoba and Winnipeg with Beausejour picking up 1.5 mm of rain off Lake Winnipeg this morning.

With such a cool airmass in place, it would seem likely that frost would be a concern for tonight.. However, a storm system from the west is expected to bring increasing clouds overnight with increasing southeasterly winds that should minimize the threat of frost over southern MB tonight. However, look for a chilly evening with patchy frost possible mainly east of Winnipeg. This storm system by the way may bring the season's first snowfall over central AB and SK tonight through Wednesday night!

Thursday, September 06, 2007

Well, school's back.. and so is the PJ weather station.. another Charleswood area weather site. The station is located on the roof of Pacific Junction School on Cathcart Ave next to the Assiniboine Forest south of Grant. The station is a good alternate site to Rob's Obs for real time weather data in Charleswood. Note the PJ site has better exposure on top of the roof, so wind readings from their station are more accurate than mine, which tends to register on the low side due to the sheltering effects of houses and trees.